I have had the same problem and it is easy to fix.
You need a more senior user to do this and the only one higher than admin is system, to get access to this you will have to hack vista's logon.
Boot vista installation disc and go to repair.
Open command prompt and type notepad.
In notepad click on file and the on open.
In the box go to C:Windowssystem32 and change document type to all file.
Find file sethc.exe and rename it to sethc.exe.old
Copy cmd.exe and paste it. It will be called "Copy of cmd.exe".
Rename "Copy of cmd.exe" to sethc.exe.
Restart your PC.
Upon logging in, press SHIFT 5 times and cmd will nou apear.
In cmd type "Net user administrator *".
Then type new password.
PS. No character will show when you type new password
Thanks to Happy Hacker for this tip on the forum.